Abstract
We describe the syntheses and crystal structures of two indole derivatives, namely 6-isopropyl-3-(2-nitro-1-phenyl-eth-yl)-1H-indole, C19H20N2O2, (I), and 2-(4-meth-oxy-phen-yl)-3-(2-nitro-1-phenyl-eth-yl)-1H-indole, C23H20N2O3, (II); the latter crystallizes with two mol-ecules (A and B) with similar conformations (r.m.s. overlay fit = 0.139 Å) in the asymmetric unit. Despite the presence of O atoms as potential acceptors for classical hydrogen bonds, the dominant inter-molecular inter-action in each crystal is an N-H⋯π bond, which generates chains in (I) and A+A and B+B inversion dimers in (II). A different aromatic ring acts as the acceptor in each case. The packing is consolidated by C-H⋯π inter-actions in each case but aromatic π-π stacking inter-actions are absent.
Highlights
We describe the syntheses and crystal structures of two indole derivatives, namely 6-isopropyl-3-(2-nitro-1-phenylethyl)-1H-indole, C19H20N2O2, (I), and
2-(4-methoxyphenyl)-3-(2-nitro-1-phenylethyl)-1H-indole, C23H20N2O3, (II); the latter crystallizes with two molecules (A and B) with similar conformations (r.m.s. overlay fit = 0.139 Å) in the asymmetric unit
Spectroscopy (Muñoz et al, 2004), and such bonds have been observed in many crystal structures of indole derivatives (e.g. Krishna et al, 1999; Cordes et al, 2011)
Summary
N—H interactions are a well-recognised type of ‘nonclassical’ weak bond (Desiraju & Steiner, 1999). They are of special significance in biological systems (Burley & Petsko, 1986; Levitt & Perutz, 1998) and are thought to play an important role in establishing protein secondary structures (Lavanya et al, 2014). They may even influence the chargetransport properties of organic semiconductors (Zhao et al., 2009). The molecular structure of (I), showing 50% probability displacement ellipsoids
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